Photochemistry of 4-Thia-2-cycloalkenones. Part 2

Methyl 2-allyl-3-oxo-2,3-dihydrothiophene-2-carboxylate ( 2 ) photocyclizes selectively to methyl 2-oxo-7-thiatricyclo3.2.1.0^3,6]octane-1-carboxylate ( 4 ). In contrast, 4-thia-2-cyclohexenone 3 , on irradiation, affords only low yields of dimers, cycloadducts (2-methylpropene) or RH reduction products (i-ProH).